TIME TRAVEL
There are two known ways of traveling backwards or forwards in time, in the Stargate universe. One is to simply use Ancient technology. Around 10,000 years ago, an Ancient scientist named Janus devised a mechanism for targeted time travel, equipping a small Puddle Jumper ship with the device.
When the Atlantis expedition arrived from Earth, Elizabeth Weir inadvertently used the ship to travel 10,000 years into the past, where she met Janus and helped to save the city (“Before I Sleep”). A second time-traveling Jumper turned up in the Milky Way Galaxy, which SG-1 recovered (“It’s Good To Be King”) and later used to steal a Z.P.M. power source from Ra, during his rule on earth 5,000 years ago (“Moebius”).
There is another way to travel through time, however — though it is much less precise. The Stargate creates an artificial wormhole between two planets, but when that wormhole passes too closely to the magnetic field generated by a solar flare, the wormhole’s path through space-time is disrupted. The greater the magnitude of the flare, the greater the temporal variance. In such cases, a traveler would step through the gate on one side and emerge through the destination gate years or even millennia before or after he left.
It is extremely rare that this phenomenon would ever interfere with normal gate travel, since solar flares last only a few seconds and wormholes don’t always pass close enough to a star to be affected. But it has occurred twice in the 11-year history of Earth’s Stargate program.
Just two years into the program, SG-1 stepped through the S.G.C. gate only to find themselves emerging back on Earth, in the year 1969 (“1969”). This particular solar flare had not only caused a temporal variance, but caused the wormhole to bend back on itself and reconnect to the Earth Stargate in the past, rather than taking SG-1 to its destination. Because they had a tip on the exact moment of another flare, however, they could use the gate to return home.
The second event took place 10 years later, when John Sheppard made a routine trip from a planet in the Pegasus Galaxy back to Atlantis. The flare sent him tens of thousands of years into the future, to a time when the city had been abandoned and the ocean turned to desert (“The Last Man”).
John was able to return to his proper time because the Ancient city has long-range sensors capable of detecting solar flares. This technology is simply beyond Earth’s capabilities; since light even from our own sun takes 8 minutes to reach Earth, by the time a flare of sufficient magnitude has been detected, it’s already too late to use it to travel through time.
But other alien technology has been able to accomplish this feat. When the Aschen occupied Earth in an alternate time line (“2010”), Samantha Carter used their advanced sensor technology to determine the time of a flare that would let them send a message back to themselves 10 years earlier … warning Stargate Command to avoid contact with the Aschen altogether.
To practically use the Stargate for time travel, then, one must have the technology to locate a proper solar flare, and then dial the Stargate so that the wormhole path will pass closely enough to that star.